The present invention relates to an ink transfer thermal printer for forming characters, graphics, etc. as patterns of dots upon a recording medium such as recording paper, and is characterized by the use of a thermo-sensitive ink which is solid at normal ambient operating temperatures and is transferred to a recording paper by melting selected portions of the ink by localized heating.
High speed printers used in data processing applications can be basically classified into impact and non-impact printers. The highest speeds are attainable with non-impact printers, which also have the advantage of a low level of operating noise. The main types of non-impact printers in use at present are thermal printers, in which dot patterns representing characters etc. are formed by selective heating of minute areas of a thermo-sensitive recording paper, or of an ink ribbon or ink film having thermo-sensitive ink coated thereon, with portions of the thermo-sensitive ink being melted and transferred by contact to the recording paper, and ink jet printers. In the case of ink jet printers, ink stored in liquid form is selectively ejected through extremely small apertures onto a recording paper, to thereby form patterns of dots. Such a method enables a high speed of printing, since the printing head and the recording paper can be kept out of contact with one another. However since the ink is a liquid at normal temperatures, problems arise due to evaporation of the ink. Such evaporation makes storage of the ink difficult over a long time period, and in addition results in material being deposited in the ink ejection apertures which come to block these apertures. Thus, such prior art ink jet printers are basically unsatisfactory with regard to reliability and the need for frequent maintenance, and the difficulty of storing the ink.
In the case of a thermal printer which utilizes an ink ribbons or ink films, the problem arises that large amounts of consumable materials must be stored before use and disposed of after use, i.e. the used ribbons or films. Apart from the substantial cost of such materials, the necessary storage space for these is a hindrance to making such a printer compact and lightweight, and replacement of the ink ribbons or ink films is generally troublesome and timeconsuming.
One approach which has been suggested to overcome these problems of thermal printers which use ink ribbons or ink films is to utilize an endless fabric tape, upon which portions of thermo-sensitive ink are selectively deposited at a position distant from the recording paper, and then are transferred from the tape to the recording paper by rollers. However such a scheme is very complex mechanically, and so is unsatisfactory from the aspect of manufacturing cost, as well as with regard to size and weight.
It is an objective of the present invention to eliminate these disadvantages of prior art types of ink transfer thermal printer, by providing a printer which employs thermo-sensitive ink that is solid at normal temperatures, and which is utilized directly (i.e. without being formed upon some other medium such as plastic ribbon or film). Since the thermo-sensitive ink is completely consumed during the printing process, there is no need for disposal of waste materials, so that maintenance is greatly simplified, and the printer can be made compact and lightweight. In addition, since the thermo-sensitive ink is solid at normal temperatures, it can be inserted into the printer very easily, without danger of the operator's hands being soiled. Furthermore, the present invention can be adapted to provide an ink jet type of operation, in which thermo-sensitive ink that has been selectively liquified by heating is ejected through small apertures to form dots on the recording paper. In this case, since the thermo-sensitive ink is maintained in the solid state until immediately before it is consumed in the printing process, formation of undesirable materials by evaporation of the ink does not occur, so that such a ink transfer thermal printer provides much more reliable operation than has been possible with prior art types of ink jet printer using liquid ink.